Method for preventing low-temperature degradation of tetragonal zirconia containing materials

Abstract

A ceramic body has a surface region that contains tetragonal zirconia. The body is partially stabilized with yttria and, optionally, ceria. Substantially the entire surface region is composed of recrystallized tetragonal strain free grains of yttrium oxide zirconium oxide. The content of yttrium in the surface region is substantially the same as the average content of yttrium in the ceramic body, and the surface region is covered with a thin layer of stable tetragonal grains.

What is claimed is: 
     
       1. A process for preparing a ceramic body having a surface region that consists essentially of tetragonal zirconia and is partially stabilized with yttria and mixtures thereof with ceria comprising the steps of: (a) sintering the body to at least 95% theoretical density at a temperature below about 1550° C.;   (b) abrading a portion of said surface region to impart strain and deformation thereto; and   (c) heat treating said surface region to recrystallize thereon tetragonal strain free grains of yttrium oxide zirconium oxide, the content of yttrium on said surface region being the same as the average content of yttrium in said ceramic body, such that said surface region is covered with a thin layer consisting solely of tetragonal grains.   
     
     
       2. A process as recited in claim 1, in which said ceramic body has a composition consisting essentially of 2 to 3 mol % yttria, 0 to 6 wt % ceria, and 0 to 40 wt % alumina, the balance being zirconia plus incidental impurities. 
     
     
       3. A process as recited in claim 1, wherein said abrading step is carried out with a diamond wheel having a mesh size of about 120 to 600, a surface velocity of about 100 to 6000 feet per minute and a downfeed rate of about 0.001 to 0.100 mm/pass. 
     
     
       4. A process as recited in claim 1, where said abrading step is carried out with grinding media selected from the group consisting of alumina, silicon carbide, boron carbide and diamond. 
     
     
       5. A process as recited in claim 1, wherein said heat treating step further comprises the steps of: (a) heating said body at a heating rate of about 100° to 500° C./hr to a temperature within a range of about 1000° to 1400° C.;   (b) maintaining said temperature within said range for a time ranging from about 0.5 to 3.0 hrs; and   (c) cooling said body to room temperature at a cooling rate of about 200° to 600° C./hr.   
     
     
       6. A ceramic body having a surface region that consists essentially of tetragonal zirconia, said ceramic body being partially stabilized with yttria and mixtures thereof with ceria, and having substantially the entire surface region composed of recrystallized tetragonal strain free grains of yttria oxide zirconium oxide, the content of yttrium in said surface region being the same as the average content of yttrium in said ceramic body, such that said surface region is covered with a thin layer consisting solely of stable tetragonal grains. 
     
     
       7. A ceramic body as recited in claim 6, wherein said surface region is substantially 100% in the tetragonal lattice modification and said recrystallized tetragonal strain free grains have an average grain size ranging from about 0.1 to 0.5 micrometers. 
     
     
       8. A ceramic body as recited in claim 6, wherein said layer of tetragonal grains has a thickness ranging from about 0.5 to 2 micrometers. 
     
     
       9. A ceramic body as recited in claim 8, wherein said surface region is substantially 100% in the tetragonal lattice modification. 
     
     
       10. A ceramic body as recited in claim 8 wherein said layer has a thickness ranging from about 1 to 1.5 micrometers.